1. Field of Invention
The present invention relates to a precision fullwave rectifier which is used in communication systems or non-linear signal processors.
2. Discussion of Related Art
FIG. 1 shows a circuit for a precision fullwave rectifier using operational amplifiers according to a related art.
Referring to FIG. 1, a precision fullwave rectifeir 10 of a related art amplifies an alternating current input voltage Vin by operational amplifiers and rectifies the current by diodes.
More specifically, a negative input terminal of a first operational amplifier AMP1 receives an input voltage through a first resistor R1 while a positive input terminal is connected to the ground through a sixth resistor R6.
A first diode D1 is connected backward between an output stage and the negative input terminal of the first operational amplifier AMP1, while a second diode D2 is connected forward between the output stage and the negative input terminal.
An output of the first operational amplifier AMP1 is connected to a negative input terminal of a second operational amplifier AMP2 from a node between a second resistor R2 and the first diode D1 through a third resistor R3, and a wave-rectified output is outputted from an output terminal of the second operational amplifier AMP2. An alternating current input voltage Vin is connected to a negative input terminal of the second operational amplifier AMP2 through a fourth resistor R4, while a positive input terminal of the second operational amplifier AMP2 is connected to the ground through a seventh resistor R7. Besides, a fifth resistor R5 is connected between the output stage and the negative input terminal of the second operational amplifier AMP2.
The first, third, and fourth resistors R1, R3, and R4 are equal to one another in resistance, while the resistance of the second resistor R2 is twice larger than that of the first, third or fourth resistor R1, R2 or R4.
The precision fullwave rectifier of the related art is operated as following.
When the alternating current input voltage Vin is a positive pulse(i.e., the voltage has a positive value), the first diode D1 is turned `on` while the second diode D2 is turned `off`. EQU Vamp1=-Vin.multidot.(R2/R1) (formula 1-1)
In the above formula 1-1, an output of the first operational amplifier AMP1 is an inverted negative pulse(i.e, a negative value) having a predetermined gain(Av=R2/R1) EQU Vamp1+Vin=-Vin.multidot.(R2/R1-1) (formula 1-2)
The output of the first operational amplifier AMP1 as well as the positive pulse of the initial alternating current input voltage Vin is inputted to the negative input terminal of the second operational amplifier AMP2.
Namely, an output Vout of the second operational amplifier AMP2 is inverted to be outputted as a positive pulse, which is shown in the following formula. ##EQU1##
When the alternating current input voltage Vin is a negative pulse(i.e., a negative value), the first diode D1 is turned `off` while the second diode D2 is turned `on`. EQU Vamp1=-Vin.multidot.(0/R1) (formula 1-4)
Accordingly, an output of the first operational amplifier AMP1, as shown in formula 2-1, is connected virtually to the negative input terminal, becoming 0.
Moreover, a negative pulse of the alternating current input voltage Vin is inputted to the negative input terminal of the second operational amplifier AMP2.
In this case, the output Vout of the second operational amplifier AMP2 is as following. EQU Vout=-Vin.multidot.(R5/R4) (formula 1-5)
Namely, the negative pulse is inverted to be outputted as a positive pulse, thereby operating wave rectification of the alternating current input voltage.
Unfortunately, the precision fullwave rectifier using operational amplifiers of the related art requires a plurality of resistors consisting of a plurality of pairs, two operational amplifiers, and two diodes, which is unable or impossible to be embodied on an integrated circuit. Moreover, the rectifier of the related art consumes too much power, occupies a large layout area, and has an operational speed limited by the operational amplifiers.